Method and device at a transmitter and receiver unit in a mobile telephone system

ABSTRACT

A method and apparatus for providing communication signals via air or other ducting in a building. Two-way mobile telephone communications between a mobile telephone in a building and an antenna in one or more air ducts may be provided. In one embodiment, wireless communication between at least two antennas in a ventilation duct and rooms and spaces in a building may be provided without the use of bi-directional couplers or re-radiators. In another embodiment, a first signal may be emitted from an antenna in a ventilation duct of a building and the first signal transmitted by the duct for passage through an opening into a room or space in the building. A second signal may be received into the duct through the opening and transmitted by the duct from the opening for reception by the antenna.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/SE99/01770, filed Oct. 5, 1999, which claims priority to Swedishpatent application 9901085-2, filed Mar. 24, 1999.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a method pertaining to a transmitterand receiver unit in a mobile telephone system. The invention alsorelates to an arrangement for carrying out the method.

More specifically, the invention relates to a method and to anarrangement for mobile telephone systems in large buildings, andparticularly in very tall buildings such as so-called skyscrapers. Themobile telephone system may be any known wireless mobile system, forinstance a GSM system. The invention is described below with referenceto a GSM system, although it will be understood that the invention isnot restricted to this particular type of system. For instance, thesystem may be a PABX system or a wireless-LAN-system. The presentinvention can also be applied in fully internal wireless mobiletelephone systems in large buildings, where the internal system isconnected to the outside world via an existing telephone network.

2. Description of Related Art

The use of a mobile system in large buildings, and then particularly inskyscrapers, presents serious problems unless measures are taken in thebuildings concerned. This is due to several reasons. One reason is theactual building itself, since a skyscraper will normally include asignificant number of reinforcement bars, steel beams, etc., which tendto screen the building magnetically from the outside world. The metalcoated panes of facade glass with which such buildings are normallycovered to a large extent also have this affect. It is also necessary ina high building to install a large number of base stations whichcommunicate with the mobile telephones and which are able to cover thewhole of the building area. This can present a system problem withrespect to the base station with which a given mobile telephone shallcommunicate.

Another problem is one of providing effective radio coverage withinlarge buildings. When ground-mounted base stations are used, this is dueto attenuation of the radio signals caused by the building, andconsequently coverage will become poorer further into a building. Byground-mounted base stations is meant base stations that are placedoutdoors.

A further problem resides in the requirement of a high network capacityin large buildings, owing to the large number of users in suchbuildings. For instance, if a high building has good radio contact withground base stations the users in said building will take a large partof the capacity of such base stations, therewith reducing the basestation capacity for users outside the building. Furthermore, there willoften be interference between different base stations covering thebuilding, resulting in poor speech quality and, at times, in lostconnections.

Consequently, mutually separate internal mobile telephone systems areoften installed in large and high buildings.

Skyscrapers and large buildings have been mentioned in the aforegoing.By large buildings is also meant large public complexes or buildings,such as airport buildings, railroad stations, restaurants, officebuildings, and so on.

SUMMARY OF THE INVENTION

The present invention is not restricted to any particular type ofbuilding, but can be applied in all manner of buildings which due totheir size and/or configuration necessitate the installation of separatesystems that include comprehensive cabling, a large number of antennas,etc., when practicing known techniques, in order to obtain satisfactorymobile telephone traffic with good coverage within the buildingconcerned. What is strived for is higher speech quality, better coverageand greater capacity.

Such separate installations include a local transceiver unit which isconnected to the fixed part of a mobile telephone network installed inthe building. The transceiver unit is a base transceiver station thatcorresponds to a typical base station in a GSM network. Cables are drawnfrom the transceiver unit to different stories or floors in thebuilding, where one or more antennas are placed on each storey.

According to one embodiment, coaxial cables are drawn from thetransceiver unit to passive antennas in the building, via so-calledsplitters. This solution is primarily intended for smaller buildings. Itis not as effective in larger buildings, due to the high lossesexperienced in the coaxial cables, among other things.

Consequently, fibre optic cables are used in larger buildings betweenthe transceiver unit and an active antenna unit at each storey, forinstance. The active antenna unit converts light in the fibre opticcable to an RF-signal and vice versa, in addition to including atransceiver antenna. An installation of this nature may also besupplemented with a facility in which the active antenna unit alsosupplies passive antennas via splitters.

It is obvious that the known solutions to the problem of implementingmobile telephone systems in large buildings requires a large amount ofcoaxial cables and fibre optic cables to be laid in the building, andthat a large number of splitters, combiners, antenna units and antennasmust be installed. Such installation is very laborious andcost-demanding.

The present invention solves the aforesaid problems in a very simple andrelatively very inexpensive manner.

The present invention thus relates to a method pertaining to atransceiver unit in a mobile telephone system in which the transceiverunit is installed in a building that includes a ventilation system foruse for mobile telephone traffic within the building, said method beingcharacterised by installing one or more antennas in one or more of theair ducts belonging to the building ventilation system and connectingsaid antennas to said transceiver unit.

The invention also relates to an arrangement that has essentially thecharacteristic features set forth in claim 7.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to anexemplifying embodiment of the invention and also with reference to theaccompanying drawing, in which

FIG. 1 is a schematic illustration of a skyscraper building;

FIG. 2 is a schematic illustration of a ventilation system in the formof an air-conditioning system, and is a sectional view of the stories ofa skyscraper building;

FIG. 3 is a schematic, diagrammatic illustration of an installation in abuilding; and

FIGS. 4-6 show alternative antenna installations.

DETAILED DESCRIPTION

The invention is described below with reference to a skyscraper,although it will be understood that the invention can be applied equallyas well in other types of building, as mentioned earlier.

FIG. 1 illustrates a typical skyscraper 1. Three particular stories 2,3, 4 are marked in FIG. 1. These stories are used for anair-conditioning plant, and the supply of electric current and water.With respect to the air-conditioning system, an air-conditioning plantinstalled on such a storey, or floor, will normally serve a number ofbuilding stories, or floors, above and below the air-conditioning plant,as illustrated by the arrows 5, 6, 7. An air-conditioning plant may, forinstance, serve six stories below the plant and six stories above thestorey on which the plant is installed.

Instead of an air-conditioning plant, the system concerned may be ageneral ventilation system or a ventilation system for ventilation onthe one hand and for heating the building on the other hand.

FIG. 2 is a schematic illustration of an air-conditioning plant 8 whichdistributes supply air and exhaust air to and from the various storiesor floors via main air ducts 9, 10.

Provided on each storey is a secondary air duct 11, 12 which isconnected to the main air duct 9, 10 and which distribute air torespective stories.

An air conditioning system includes a duct system 12, 10 which deliversair to different parts of the building, and a duct system 11, 9 whichsucks air from different parts of said building. A blower 13 blows airinto the air supply ducts. Exhaust air normally passes through a filter14, before being released. The direction in which the air flows isarrowed in FIG. 2. A cooling and/or heating coil 15 is connected to theunit 8, for adjusting the temperature of the supply air. The design ofan air-conditioning plant will, of course, vary in accordance with thesize and geographical location of the building.

The various spaces, rooms, in the building will include openings throughwhich air can enter and leave the space concerned. In an air-conditionedbuilding, the openings are normally positioned to achieve a uniform airflow throughout the entire building. Such openings are normally placedin all rooms and in other spaces in the building.

The present invention relates to a method pertaining to a transceiverunit in a mobile telephone system in which the transceiver unit 16 isinstalled in a building for use in mobile telephone traffic within thebuilding, and in which the building is provided with a ventilationsystem of known kind.

The transceiver unit 16 is of a known kind, such as a so-called basetransceiver station, and is connected to the mobile telephone networkconcerned, normally via a fixed communications network. The transceiverunit 16 can be placed anywhere in the building, and more than onetransceiver unit may be placed in the building.

According to the present invention, one or more antennas 17, 18 is/areinstalled in one or more of the air ducts 9, 10 of the buildingventilation system, such as an air-conditioning system. Theantenna/antennas 17, 18 is/are connected to the transceiver unit 16,this connection between antenna and transceiver unit being shownschematically by the chain line 19 in FIG. 2.

The antennas are, for instance, of the kind used for mobile telephones,i.e. omnidirectional antennas. It will be understood, however, thatother antennas may be used when applying the present invention. Forinstance, antennas that have a directional effect may alternatively beused. For example, an antenna is installed by providing in the air ducta hole through which the antenna can be inserted. Alternatively, anantenna is installed in the air duct and held in place by means of anappropriate fastener.

In one preferred embodiment of the invention, at least one antenna isinstalled in a main air duct 9, 10, as illustrated with the antennas 17,18 in FIG. 2. The main air ducts communicate with a number of smaller orsecondary air ducts 11, 12 which open into different rooms in thebuilding. The grating normally located adjacent the orifice ofrespective air ducts 11, 12 in a room or some other space in thebuilding shall be designed to allow the radio signals concerned to passfreely through said orifice. This requirement is satisfied by usingplastic gratings.

The antennas have, for instance, a transmission power of only 0.5 W at atransmission frequency of 1800 MHz. Trials with such antennas andconventional GSM telephones have shown that extremely effective contactis obtained between the antennas and mobile telephones in a building inwhich the present invention has been applied in the aforedescribedmanner.

However, the person skilled in this art will realise that frequency andoutput power can be chosen in accordance with the radio system to beused.

Because the antennas are placed centrally in the air-conditioningsystem, a signal sent by the transceiver unit via the antennas willpropagate generally equally throughout that part of the building towhich the main air ducts concerned extend. Similarly, a signal sent by amobile telephone will be conducted via an orifice of said kind in abuilding space into a smaller air duct 11, 12 and through said duct to amain air duct 9, 10 and therewith to an antenna 17, 18.

In one embodiment of the invention, at least one antenna is installed ineach section 5, 6, 7 of the air ducts 9, 10 of the air-conditioningsystem, where each of said sections serves a given number of stories, orfloors, in the building. One such section may conveniently include from12 to 24 stories of a skyscraper, although it will be understood thatthe number of stories served will depend on the design of theair-conditioning system.

When many stories are served by one and the same main air duct, it ishighly beneficial to install one or more additional antennas in eachsection of the air ducts 9, 10 of the air-conditioning system, whereeach of the sections serves different parts of the building. This isillustrated in FIG. 2 with the additional antennas 20, 21.

According to one preferred embodiment, one or more antennas areinstalled in the supply air ducts 10 and one or more antennas areinstalled in the exhaust air ducts 9. Because the orifices of the supplyair system and the exhaust air system respectively in the various spacesof the building are often positioned at different places in said spaces,this embodiment provides effective and uniform radio coverage.

In one embodiment, the antennas 17, 18, 20, 21 are passive antennas andare connected to the transceiver unit 16 via coaxial cables 22, 23, asillustrated in FIG. 3.

Alternatively, the antennas 24, 25 are active antennas which areconnected to the transceiver unit 16 via fibre optic cables 26, 27. Inthis case, the active antennas include a device 28, 29 which convertslight in the fiber optic cable to an RF-signal and vice versa, inaddition to including a transmitting and receiving antenna.

FIGS. 4, 5 and 6 illustrate alternative antenna installations in airducts 9, 10.

FIG. 4 shows an antenna 30 which is housed in a metallic housing 31. Anopening has been made in the duct and covered with a non-metallic cover32, for instance a plastic cover. The cover 32 and the housing 31 aresecured in the duct 9, 10 by means of a screw joint 33, 34. The antenna30 may be a directional antenna or some other suitable type.

FIG. 5 shows an antenna 35 which is carried by a plate 36 that covers anopening in the air duct 9, 10. The plate 36 is secured to the duct 9, 10by means of a screw joint 33, 34. The antenna is suitably anomnidirectional antenna.

FIG. 6 shows an antenna arrangement in which the antenna 37 projectsinto the air duct 9, 10. The antenna 37 is secured to the duct 9, 10 bymeans of a screw joint 33, 34. The antenna may be a dipole antenna orsome other suitable type.

Both active and passive antennas may be used in one and the same systemand placed at mutually different positions.

The person skilled in this art will have no trouble in determining thenumber of antennas required and their positions in the air ducts inobtaining the desired radio coverage.

It will be obvious that the present invention requires a minimum ofinstallations in a building in comparison with the installationsrequired when applying the aforedescribed known technology, by virtue ofthe fact that the existing air duct infrastructure of a building is usedas wave guides.

The present invention thus provides a significant advance in enablinghighly effective radio coverage for mobile telephony to be obtained in abuilding quickly and inexpensively, and also to provide very high speechquality and high capacity.

Although the invention has been described with reference to a number ofembodiments and with reference to only one section of anair-conditioning system, it will be understood that the invention can bevaried in different ways to achieve the radio coverage desired. Insteadof placing antennas in air-conditioning duct sections that lie atdifferent heights above each other, the antennas may equally as well beplaced in different sections of air-conditioning ducts that are locatedhorizontally one after the other, as in a large, elongated air terminalbuilding.

The present invention shall not therefore be considered as limited tothe aforedescribed exemplifying embodiment, since variations can be madewithin the scope of the accompanying claims.

What is claimed is:
 1. A method relating to a transceiver unit in a mobile telephone system wherein the transceiver unit is installed in a building and used for mobile telephone traffic within the building, and wherein the building includes a ventilation system, the method comprising: providing one or more antennas in a location to transmit and receive signals in one or more air ducts belonging to the ventilation system of said connecting said antenna or antennas to the transceiver unit; wherein two-way wireless mobile telephone communication between at least one mobile telephone device in a room or space in the building and at least one antenna via the one or more air ducts acting as a waveguide for the wireless mobile telephone communication is enabled.
 2. A method according to claim 1, characterized by providing at least one antenna in communication with a main air duct that communicates with a plurality of smaller or secondary air ducts which open into rooms and spaces in the building.
 3. A method according to claim 1, characterized by providing one or more antennas in communication with each of a plurality of sections of the air ducts of said ventilation system where each of said sections serves a respective different part of the building.
 4. A method according to claim 1, characterized by providing one or more antennas in communication with air ducts that deliver supply air to the building and providing one or more antennas in communication with exhaust air ducts.
 5. A method according to claim 1, characterized in that one or more antennas are passive antennas connected to the transceiver unit via coaxial cables.
 6. A method according to claim 1, characterized in that one or more antennas are active antennas connected to the transceiver unit via fiber optic cables.
 7. The method according to claim 1, wherein wireless signals transmitted by a mobile telephone device in a room or space in the building are received into the one or more air ducts through an opening in the one or more air ducts that is transparent to the wireless signals.
 8. The method according to claim 1, wherein wireless signals transmitted by a mobile telephone device in a room or space in the building are introduced into the one or more air ducts without the use of an antenna positioned in the one or more air ducts.
 9. An arrangement relating to a transceiver unit in a mobile telephone system in which said transceiver unit is installed in a building and used for mobile telephone traffic within said building, and wherein the building includes a ventilation system, characterized in that one or more antennas is/are installed to transmit and receive signals in one or more air ducts belonging to the ventilation system of said building and connected to the transceiver unit, wherein two-way wireless mobile telephone communication between at least one mobile telephone device in a room or space in the building and at least one of the antennas via the one or more air ducts acting as a waveguide for the wireless mobile telephone communication is enabled.
 10. An arrangement according to claim 9, characterized in that at least one antenna is installed in communication with a main air duct that communicates with a number of smaller or secondary air ducts which open into different rooms and spaces in the building.
 11. An arrangement according to claim 9, characterized in that one or more antennas are installed in communication with each of a plurality of sections of said ventilation system, where each of said sections is intended to serve a different part of the building.
 12. An arrangement according to claim 9, characterized in that one or more antennas are installed in communication with air supply ducts for delivering supply air to the building; and in that one or more antennas are installed in communication with exhaust air ducts.
 13. An arrangement according to claim 9, characterized in that one or more of the antennas are passive antennas connected to the transceiver unit via coaxial cables.
 14. An arrangement according to claim 9, characterized in that one or more of the antennas are active antennas connected to the transceiver unit via fiber optic cables.
 15. The arrangement according to claim 9, wherein wireless signals transmitted by a mobile telephone device in a room or space in the building are received into the one or more air ducts through an opening in the one or more air ducts that is transparent to the wireless signals.
 16. The arrangement according to claim 9, wherein wireless signals transmitted by a mobile telephone device in a room or space in the building are introduced into the one or more air ducts without the use of an antenna positioned in the one or more air ducts.
 17. A method for directing radiation through the ventilation system of a building comprising: placing at least two antennas in a position relative to an air duct of the ventilation system to introduce radiation into the ventilation system; connecting the at least two antennas to a transceiver; and providing wireless communication between the at least two antennas and communication devices in rooms and spaces in the building via the air duct, wireless communication signals being carried in the air duct acting as a waveguide without the use of a bidirectional coupler or re-radiator positioned in the air duct between the communication devices and the at least two antennas.
 18. The method as claimed in claim 17, wherein the step of placing includes placing at least two antennas in each of a plurality of air ducts of the ventilation system.
 19. The method as claimed in claim 18, wherein the step of placing further includes placing a plurality of antennas in each of the plurality of air ducts in the ventilation system.
 20. A ventilation system of a building comprising: a plurality of air ducts having sections that each serve a respective different part of the building; and at least one antenna positioned relative to each of the sections of the air ducts, and connected to a transceiver in order to introduce radiation into the ventilation system and provide two-way wireless communication between a respective different part of the building and the transceiver via a respective section of the air ducts that acts as a waveguide for signals transmitted by the at least one antenna and for signals transmitted from parts of the building outside of the air ducts.
 21. A ventilation system as claimed in claim 20, wherein the ventilation system includes at least one antenna in communication with each of the air ducts.
 22. A ventilation system as claimed in claim 21, wherein the ventilation system includes a plurality of antennas in communication with each of the air ducts.
 23. A ventilation system as claimed in claim 20, wherein the at least one antenna wirelessly communicates with a device located in a room or space of the building by emitting a signal that is carried in at least one section of the air ducts and passes into the room or space through an opening in the at least one section of the air ducts to be received by the device, and by receiving a signal that is transmitted by the device, passes through the opening in the at least one section of the air ducts and is carried in at least one section of the air ducts to the at least one antenna.
 24. A method of providing wireless communications, comprising: providing at least one antenna in communication with at least one air duct that is part of a ventilation system in a building; emitting a first signal from the at least one antenna; transmitting the first signal in the at least one air duct acting as a waveguide between the at least one antenna and an opening in the at least one air duct, the opening being transparent to the first signal; passing the first signal through the opening into a room or space in the building to be received by a wireless communication device; receiving a second signal transmitted by the wireless communication device through the opening into the at least one air duct; transmitting the second signal in the at least one air duct acting as a waveguide between the opening and the at least one antenna; and receiving the second signal at the at least one antenna.
 25. The method of claim 24, wherein the step of transmitting the first signal comprises: transmitting the first signal from the antenna to the opening without the use of a bi-directional coupler or a re-radiator; and the step of and transmitting the second signal comprises: transmitting the second signal from the opening to the antenna without the use of a bi-directional coupler or a re-radiator.
 26. The method of claim 25, wherein the step of providing at least one antenna comprises: providing at least two antennas in communication with at least one air duct.
 27. A method of providing wireless communications, comprising: providing at least one antenna in communication with at least one air duct that is part of a ventilation system in a building; receiving a wireless signal transmitted by a wireless communication device in the building through an opening in the at least one air duct; transmitting the wireless signal in the at least one air duct acting as a waveguide between the opening and the at least one antenna; and receiving the wireless signal at the at least one antenna. 